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'optoisolator, simple explanation'
1998\04\27@162447 by PHXSYS

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I was hoping someone could provide a simple explanation of an optoisolator and
an example of its practical use.


Jon

1998\04\27@194125 by Sean Breheny

face picon face
At 02:24 PM 4/27/98 EDT, you wrote:
>I was hoping someone could provide a simple explanation of an optoisolator
and
>an example of its practical use.
>
>
>Jon
>

Hi Jon,

       An optoisolator is a LED/phototransistor pair typically enclosed in a DI
P8
plastic package. The LED and phototransistor are electrically isolated from
each other but the light from the LED is allowed to pass thru to the
phototransistor. All external light is shielded by the package. The pins of
the LED and phototrans are brought out on the pins of the package. So, when
you turn on the LED, the phototransistor turns on.
       The purpose is to allow information exchange from one circuit to another
without any electrical connection. The purpose of this might be to protect
a sensitive circuit from high voltages (i.e., a circuit which produces and
uses HV needs to communicate with a PIC, for example). It also might be to
prevent coupling of additional signals which might occur over wires going
between the two circuits, but which can be prevented from being transmitted
through the LED.
       So, if you were building a circuit which, say, allowed a PIC to count th
e
RPM of your car's engine via the spark plug voltage, you might  make a
small circuit which turned on the LED whenever the spark plug fired, and
then use the PIC attached to the phototransistor to count the pulses. The
advantage of doing this versus some type of direct connection is that it is
easier and more reliable to make the LED immune to voltage spikes
(especially unexpected ones) than it is to try to allow the PIC to handle
them.

Good luck,

Sean

+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
Fight injustice, please look at
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Phone(USA): (607) 253-0315

1998\04\27@210610 by Alan G. Smith

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face
Sure, I'll give it a shot.

An optoisolator is basically like an LED and a phototransistor next to each
other.

This lets you communicate information optically so electrical noise doesn't
cross the circuit.  An example of using this would be to power a relay so
that the switching didn't affect the micro that was driving it.

HTH,

Alan G. Smith
+---------------------------------------------------------
| Alan G. Smith
| .....agsKILLspamspam@spam@poboxes.com
| http://www.innovatus.com/ags

-----Original Message-----
From: PHXSYS <PHXSYSspamKILLspamAOL.COM>
To: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Date: Monday, April 27, 1998 4:27 PM
Subject: optoisolator, simple explanation


>I was hoping someone could provide a simple explanation of an optoisolator
and
>an example of its practical use.
>
>
>Jon
>

1998\04\28@094516 by Scientific Measurement Group

flavicon
face
Jon:

An optoisolator is a device which transfers information by means of a beam
of light (usually in the infrared range) from an emitting diode to a
detecting diode or transistor or thyristor device. The diode circuitry is
electrically independent (isolated) from the transfer device (diode,
transistor or thyristor).  The only thing that links the input event to the
detecting system is the beam of light so the two systems can have
independent power circuits.  If this is too basic, and you really want the
answer in terms of the physics of the phenomenon, I appologize. Let me
know.

----------
> From: PHXSYS <PHXSYSspamspam_OUTaol.com>
> To: @spam@PICLISTKILLspamspamMITVMA.MIT.EDU
> Subject: optoisolator, simple explanation
> Date: Monday, April 27, 1998 1:24 PM
>
> I was hoping someone could provide a simple explanation of an
optoisolator and
> an example of its practical use.
>
>
> Jon

1998\04\28@094516 by Scientific Measurement Group

flavicon
face
Jon:

An optoisolator is a device which transfers information by means of a beam
of light (usually in the infrared range) from an emitting diode to a
detecting diode or transistor or thyristor device. The diode circuitry is
electrically independent (isolated) from the transfer device (diode,
transistor or thyristor).  The only thing that links the input event to the
detecting system is the beam of light so the two systems can have
independent power circuits.  If this is too basic, and you really want the
answer in terms of the physics of the phenomenon, I appologize. Let me
know.

----------
> From: PHXSYS <KILLspamPHXSYSKILLspamspamaol.com>
> To: RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU
> Subject: optoisolator, simple explanation
> Date: Monday, April 27, 1998 1:24 PM
>
> I was hoping someone could provide a simple explanation of an
optoisolator and
> an example of its practical use.
>
>
> Jon

1998\04\28@094519 by Scientific Measurement Group

flavicon
face
By the way, I forgot to mention that one example of a practical use for the
optoisolator would be detecting 120 Volt AC signal and sending the
information to a measurement system.  But You can probably think of many
better uses.

----------
> From: PHXSYS <spamBeGonePHXSYSspamBeGonespamaol.com>
> To: TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU
> Subject: optoisolator, simple explanation
> Date: Monday, April 27, 1998 1:24 PM
>
> I was hoping someone could provide a simple explanation of an
optoisolator and
> an example of its practical use.
>
>
> Jon

1998\04\28@094519 by Scientific Measurement Group

flavicon
face
By the way, I forgot to mention that one example of a practical use for the
optoisolator would be detecting 120 Volt AC signal and sending the
information to a measurement system.  But You can probably think of many
better uses.

----------
> From: PHXSYS <RemoveMEPHXSYSspamTakeThisOuTaol.com>
> To: PICLISTEraseMEspam.....MITVMA.MIT.EDU
> Subject: optoisolator, simple explanation
> Date: Monday, April 27, 1998 1:24 PM
>
> I was hoping someone could provide a simple explanation of an
optoisolator and
> an example of its practical use.
>
>
> Jon

1998\04\28@143503 by Andy Kunz

flavicon
face
> An optoisolator is a device which transfers information by means of a beam
>of light (usually in the infrared range) from an emitting diode to a

The other thing to keep in mind is that they are current translating
devices, not voltage.  They are based on LEDs, so the voltage on the
photo-"base" is related to current, not voltage.

Andy


==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\04\28@154308 by Scientific Measurement Group

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face
Yes, Andy.  The bipolar devices are current devices, unlike the FET devices
which are voltage devices.  The bipolar optocoupler will draw collector
current and emitter current when forward biased.  If you series a resistor
in either C or E, you can utilize the voltage drop across the resistor as
an excitation signal. If you want to pull a current through your load,
then, of course, you don't need to translate it.  Nice to talk to you.
Thanks for the comments.

----------
> From: Andy Kunz <EraseMEmtdesignspamFAST.NET>
> To: RemoveMEPICLISTEraseMEspamEraseMEMITVMA.MIT.EDU
> Subject: Re: optoisolator, simple explanation
> Date: Tuesday, April 28, 1998 12:16 PM
>
> > An optoisolator is a device which transfers information by means of a
beam
{Quote hidden}

1998\04\28@154308 by Scientific Measurement Group

flavicon
face
Yes, Andy.  The bipolar devices are current devices, unlike the FET devices
which are voltage devices.  The bipolar optocoupler will draw collector
current and emitter current when forward biased.  If you series a resistor
in either C or E, you can utilize the voltage drop across the resistor as
an excitation signal. If you want to pull a current through your load,
then, of course, you don't need to translate it.  Nice to talk to you.
Thanks for the comments.

----------
> From: Andy Kunz <RemoveMEmtdesignspam_OUTspamKILLspamFAST.NET>
> To: RemoveMEPICLISTTakeThisOuTspamspamMITVMA.MIT.EDU
> Subject: Re: optoisolator, simple explanation
> Date: Tuesday, April 28, 1998 12:16 PM
>
> > An optoisolator is a device which transfers information by means of a
beam
{Quote hidden}

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